LNG Process Risk Safety: Modeling

LNG Process Risk Safety: Modeling and Consequence Analysis

The Risk Assessment/Analysis

Checklist

A checklist is made up of guidelines that are placed in questions or bullets in order to assist a given methodological health and safety (EHS) risks analysis (Fthenakis and Tramell, 2003).It is used in the stimulation of group discussion and thinking. The checklist is appropriately developed by a team of experts who have a prior knowledge of hazard analysis. The checklist is then used in the process of risk assessment is includes a specified list of items that are specified using a group of codes, industry safety practices and regulations. The developed checklist is important in the LNG process by enabling the conducting of self -- appraisal as well as auditing of the LNG process and facilities. An analysis of the technique reveals that the checklist method has the disadvantage of heavily influencing the accuracy and the quality of LNG risk assessment (EASH,2010)

What-if Checklist

The what-if check-list is a rather broad-based technique of hazard assessment that combines elements of creative thinking of a team of specialists using a methodological focus of a checklist that is prepared (OSHA, 2010). A selected review team is then represented using a wide range of selected disciplines such as safety. The special team is then given the basic information on the specific hazards of materials, the process technology, equipment design, procedure, incident experiment, a review of previous hazards and instrumentation control. A thorough field is also conducted when the process in operation.

The selected review team then examines the process methodologically from the time of receipt of raw materials up to the time the final product is delivered to the intended destination. At every step, the group then generates in a collective approach a listing of all the what-if questions that concerns the hazards as well as the safety of the entire operation. After the review team has completed the listing process of forming spontaneously generated questions, it applies a systematic process of preparing a checklist in order to simulate the additional questions. Answers are then generated for each question. A consensus is then derived for each question and answer. Recommendations then follow.

The application of what if analysis in the context of LNG process lies in the process of hazard identification (Woodward and Pitblado, 2010). It is categorized as a quantitative technique of risk assessment (Bridges,2008). In our research data, it has been used in different situations such of LNG risk assessment. It can be used in the assessment of LNG fires and explosions scenarios as indicated by Biao et al. (2010).

The HAZOP (Hazard and Operability) Method

The HAZOP concept is on the basis on the principle that it is better to employ a team approach in the process of hazard analysis since it helps in the identification of more problems as compared to when just an individual's work separately then combines their results (Acutech,2009).

Extant literature has discussed this method as indicated in the works of Mannan (2005) and CCPS (2008).The technique is applicable to various LNG processes. More specifically, it can be used on onshore LNG production units, LNG reception, and ship transfer and at the regasification terminals (Woodward and Pitblado, 2010). At its simplest form, the method can effectively be used in challenging the detailed design comprising a wide range of various deviations from the otherwise normal operations as well as to confirm the level of design conformance with standard safety requirements. It can also be used in the testing of whether the safeguards that are in place are sufficient. The noted deviations could be mechanical ones such as corrosion, less temperature or more pressure (Woodward and Pitblado, 2010).They could also be human errors or a combination of events such as faults in the control system caused by a power failure. A sample of hazard identification for LNG is shown in the Table 1 below.

Table 1: HAZOP of an LNG facility

Source: Woodward and Pitblado (2010)

Failure Mode and Effects Analysis (FMEA)

This is a methodology employed in the analysis of the potential reliability problems at an early stage of a product development lifecycle when it is still easier to initiate appropriate actions intended at overcoming the issues involved and thereby improving the reliability of the product under design (Crow, 2002).The method is used in the identification of the potential failure modes and in the determination of the effects of the failure modes on the operation of a given product such as LNG so as to identify the necessary failure mitigation actions. A crucial element of this method is the anticipation of what may go wrong with a certain product. An extensive list of all the potential failure modes is formulated by the development team. The use of FMEA in the design process helps engineers in the designing product that are failure proof and reliable. They therefore become safe and pleasing to the customers. The FMEA process captures all the historical information to be used in the future improvements of a certain product (Crow, 2002).

The use of FMEA in the LNG process of identifying mechanical and electrical failure modes as pointed out by Woodward and Pitblado (2010).

Site Selection

The site for this analysis was selected from both sea and land-based LNP storage facilities. The process of risk management involves the analysis of all aspects of potential loss. The process of managing the risk. The process of LNG site selection must use community engagement in order to identify the perfect site that must have low social and environmental sensitivity as pointed out by a 2005 BHP Billiton report (BHP,2005).

Analysis regarding site selection

An analysis of a 2005 BHP Billiton Sustainability Report 2005 reveal that the role of community and their participation is integral to the process of effectively selecting an LNG site. This is evident from the fact that in the Pilbara LNG site selection (BHP,2005),the community preferred the site and 90% of them believed that the project would benefit the area through the creation of jobs, services and infrastructure. The process of selecting an LNP site should therefore include several stakeholders and the community is the biggest contributor. The risk analysis involves the analysis of the potential loss as well as the management of the potential losses. The management of the risks is the main responsibility of the process of management of a given project. Quantitative risk analysis (QRA), which is a process of providing the particular management with various event scenarios as well as the quantification of the magnitude as well likelihood of the premeditated potential losses as pointed out by Woodward and Pitblado (2010). The emphasis is however placed on the specific accidents incurred upon the initiation of a venture. These include:

1. Market risk-which are the risks that occur whenever the demand declines for a particular product

2. The currency risks-which are the losses that are a result of participating in foreign purchases and sales as a result of unfavorable shift in the level of currency exchange.

3. Property rights risks-which are the losses that associate with the taxation imposed by foreign government on investments as a result of high taxation, low incentives and upholding of contracts.

4. The natural losses as a result of hurricanes, tornadoes as well as earthquakes.

These are the risks associated with natural events.

5. The business interruption risk -- which are losses associated with the production as a result of serious mechanical failure and other factors such as political instability

Losses by accidents; these involve losses caused by incidents such as ship collision as well as grounding, operating mistakes, process equipment loss as a result of containment by corrosion as well as random failures of components.

6. Deliberate sabotage as well as acts of terrorism-This form of losses does fall outside the usual random event distribution. These losses pose serious threat to a business as well as the general community.

7. Community benefit to risk ration: which is a ratio which gauges if the investment is favorable to the community

8. Litigation potential: which is a measure of how reasonable the demands that are placed on a particular company and how they will injure the various parties that are to be compensated.

9. Measures aimed at reducing the frequency of accidents; which is the addition of speed limits, the addition of barriers and the increasing the frequency of equipment inspection

10. Measures aimed at reducing the consequences of accidents- which is the provision of protective equipment such as gloves, safety glasses as well as fire resistant clothing in order to ensure that the inventory of hazardous materials is reduces. This also includes the offsetting of the plant from residents and the addition of water spray deluge systems.

11. Insurance-this is the measure how much insurance one should buy and the fair price for obtaining that insurance.

Hazard

A physical situation that has a potential for causing human injury as well as damage to property and environment

Major Hazard

This is a term for a large scale hazard that has the potential of causing a significant amount of human harm.

The main hazards related to LNG include:

Rupture due to Corrosion

Rupture while excavation

Rupture while excavation

Rupture during an earthquake

Rupture due to mechanical failure

Rupture at compressor

Rupture at inspection stations

Uncontrolled detonation of explosives

Blow-out of gas at head and subsequent fire

Gas leak from infrastructure

Fire involving combustible

Construction damage

LPG or Diesel

Diesel pump fire involving equipment brittle fracture valve Leaks

Welding failure welding casting failure

Mechanical overstressing of equipment Vibration

pump Corrosion

joint Erosion

Failure due to external loading or impact

Internal Explosion

Underground pipe rupture of transmission pipeline

Pipe rupture at main line valve sites.

Rupture of adjacent gas pipeline

Uncontrolled detonation of explosives

Gas leak from pipeline infrastructure

Drop of pipe from pipe lifts

Accommodation fire involving combustible construction LPG or Diesel

Diesel fire involving mobile fuel tanker

Uncontrolled release of LNG

Uncontrolled release of refrigerant gas

Uncontrolled release of by- product toxic gases (e.g. H2S, CO, CO2)

Plant fire involving pressure vessel of hydrocarbons

Uncontrolled release of product on production

Fire in process plant (e.g. Cable, lubrication oil, transformer etc.)

Gas explosion during maintenance or decommissioning

Fire from vapor cloud ignition during well operation

Fire from condensate ignition during well operation

Fire during well drilling

Liquid diesel release during well drilling

Fire or explosion of gaseous hydrocarbons at Production Facility or Hides Gas Conditioning Plant during operation

Fire, involving hydrocarbon liquids

Fire at Production Facility or Hides Gas-Conditioning Plant during construction

Explosion or fire along an onshore gas pipeline

Liquid hydrocarbons spill along an onshore liquids pipeline

Fuel spill during construction of onshore pipelines

Loss of liquid containment from the inner tank followed by a pool fire in the bund

Loss of vapor from the outer tank due to overpressure condition with Ignition

Condensate or LNG spill or vapor release during ship loading

Vessel grounds during inbound or outbound transit

Collision of LNG carrier, condensate tanker or tugboat with fishing boat long loss

LNG spill

An analysis of these hazards reveals that they have different severity indices in relation to the extent of damage they can cause to the facility, community and the business. Their rates of probability also vary. Their failure effect and hazard rates also vary. The failure effects of the various LNG hazards range from 5% to 90% which are considered critical and severe respectively in terms of severity class. This shows that a lot of care must be take to curtail this wide range of hazards resulting due to LNG incidents.

Risk Analysis

This is a systematic utilization of the available information used for the identification of hazards so as to estimate the level of risk to individuals, population, environment as well as property

Risk Assessment

The overall process that is involved in the risk analysis as well as risk evaluation and usually compares the risk analysis estimates

The Liquid Natural Gas Process Chain

It was until 1964 that the Liquid Natural gas followed a process of production, import, distribution and export that followed a due sequence as illustrated in the figure below.

The Processing of LNG form extraction to consumption (Source BV -2009)

The first step in the processing chain of a natural gas is extraction. Most countries with the large natural gas reserves export this product to other countries with no reserves. The total number of these countries is 15 but the total number of the LNG plants was 22 by the beginning of the year 2008. These countries include: Indonesia, Algeria, Egypt, Russia, Qatar, Yemen, Malaysia, UAE, Nigeria, Australia, Trinidad, Brunei and Norway. Although USA also produces the natural gas, it is mainly for domestic market as their reserve is not adequate to allow exportation. In most cases the gas supply may not be enough to meet intra-country needs hence the countries import the deficit from the countries with surplus.

Once a team of Geologists and geophysicists locate a field with potential to produce the gas, a special team is sent to drill the point the prospective field to establish the viability of the quantity of the gas and if verified, the next procedure is extraction as well as processing. It is important to note that before the commercial market of the gas was established, the gas which was associated with oil, was wasted in a flare but now its value has been established and being used as LNG. There is a procedure that the natural gas must pass through in order to be fit for sale to remove impurities that are usually associated with Natural gas, which is mainly methane. Such impurities include: ethane, propane, hydrogen sulfide (H2S), Carbon dioxide (CO2), Butane, Pentane, Helium and Nitrogen as well as water and oil. These impurities must be eliminated before liquefaction to become LNG.

The Liquefaction Plant

The second stage in the process is cleaning at the liquefaction plant where a series of processing steps ensure the removal of the impure and extraneous compounds from the raw material just before liquefaction.

Purification of the product

The main reason why this purification process is necessary is that before the LNG is loaded onto tankers, trucks or ships for transportation, the composition and combustion properties must be consistently provided. This is achieved through cooling and condensation of the gas. The consistency n the content of the LNG is critical so as to obtain pipeline-quality gas which usually contains between 86% - 99% methane. It is normally associated with long-chain hydrocarbons and other impurities that fail to be removed during the processing. The figure 2 below summarizes the stripping process of removal of the compounds from the natural gas as it leaves the ground before the start of liquefaction process.

The flow process for natural purification before liquefaction (source BV -- 2009)

Carbon dioxide and water are usually removed prior to liquefaction since they can cause the malfunctioning of the liquefaction equipment due to freezing properties. Hydrocarbons with longer carbon chain like ethane, propane butane and pentane are also removed and sold as fuel to petrochemical industries.

Liquefaction

After the removal of most impurities and long-term hydrocarbons, the gas that results is mainly methane that is ready to undergo the process of liquefaction. A refrigeration technology, which is able to cool of the gas to temperatures as low as -162oC (-259oF) is used. When it liquefies, the LNG becomes a non-corrosive liquid which is as colorless as water 50% less than the weight of water. That is to say, it is half less dense than water. The LNG is more portable than the natural gas to transport since one volume of LNG is equivalent to 600 volumes of natural gas at standard temperature and pressure. This is what makes economically lucrative to transport by truck or ship.

The authors Aldwinkle and Slater (1983) had a discussion of risk and reliability analysis of the appropriate methods to be used for certain type of offshore LNG terminals, liquefaction as well as the storage ships that are secured via a single point mooring attached to an underground pipeline (Woodward and Pitblado,2010).The use of other conventional risk assessment as well as reliability methods is presented with a caveat regarding the fact that it is very difficult to estimate the failure frequencies. The tree analysis can however be used in this case provided there is relevant data. This is used in conjunction with failure mode and effect analysis (FMEA) so as to relate the consequences of the various postulated failures.

Below are the major systems that have been identified for the fault tree analysis that leads to major events of LNG gas leakage and spillage;

Liquefaction process plant failures

Single - point mooring failures

Containment system failures

LNG transfer arm failures and LNG piping system failures

They are used in the analysis of the cost/benefit ratios for the mitigation measures that are proposed. For the single - point mooring failures scenario, the mitigation usually consists of the measures that are aimed at protecting the collision of shuttle ships involved in the loading the LNG for the subsequent delivery to various markets. The options to be evaluated in this case are;

Collision barrier

Sacrificial structure.

This involves the calculation of the structure's energy - absorbing capability. This technique can be used to effectively illustrate how risk analysis can be employed in order to design structures.

Other notable contributions have been advanced for the concept of FLEX LNG and the concept of Hoegh LNG as pointed out by Pastoor et al., (2009); Festen and Leo,(2009); Iversen and Hellekleiv,(2009 ).

Transport of LNG

There are three modes of transporting the LNG which are: sea, rail and like Japan use rail. In the sea, it is transported by using specialized LNG carriers. The first transportation of LNG was done in 1959 in the Lake Charles in Louisiana and was destined to Canvey Island in the United Kingdom. The name of the voyage was MV methane. The initial stages of using the sea to transport the LNG were accompanied by training on the safety systems and also the training of the ship crews that operated the vessels. This training process has undergone improvement over the periods and now is robust in its operation. From that period, over 45,000 voyages have been carried out without losses in the LNG cargo. These days, the cargo is transported by specialized double walled ships that are designed to carry cargo at the atmospheric pressure and at a temperature of about -162oC. The carriers blends a conventional ship technology with specialized designs for handling cryogenic-temperature cargoes that isolate the LNG from the bottom as well as the sides of the hull. This is meant to conform to the International Gas Codes regulations. Some safety layers are also added to cushion the ship in case of collision. These insulating layers have also a purpose to limit the amount of LNG that evaporates throughout the voyages. While, there are about 300 ships that transport LNG daily, the International Maritime Organization (IMO) has adopted about 40 conventions as well as the protocols together with codes of conduct in the construction of equipment carrying the Liquefied gases in the seas. Due to the demand for LNG exports, the construction of the vessels for transporting LNG cargo has increased. A 135,000m3 capacity carrier costs about between $225 -- 250 million and a larger carrier costs about $300 million.

In regions around the world where the liquefaction plant is closer to the regasification facilities, trucks come in handy and cost effective means of transportation. Transportation of LNG involves the use of double-skinned special trucks to transport the liquefied gas effectively and quickly. In many areas, of the world where such trucking is done, it has become a mature industry since it began in 1968. Using tanks to transport LNG can only be limited to 20 tons by the industry regulations. The following countries have adapted tank transportation: Belgium, China, turkey, Australia, Germany, Brazil, Portugal, UK, Korea, Japan, U.S. And Norway.

The use of trucks to transport LNG is important for small scale "peak shaving" operations. This provides flexibility to the gas pipeline network. In 2003, it was noted that there were about 240 LNG facilities the world over. Of the 240, 113 were located in the U.S. And included 96 that were connected to the United States pipeline grid. The satellite LNG storage capacity came to about eighty percent of the U.S. total (IELE, 2003).

The largest of the facilities has been noted to liquefy gas that is drawn from the extensive interstate pipeline grid. However, smaller facilities that lack liquefaction capabilities do receive the commodity by trucks as pointed out by Parfomak, (2004). The LNG trucks do have a very robust construction as compared to the usual trucks for transporting fuel. The place where LNG is majorly transported by trucks is China .This is because the pipeline networks are developed well Woodward and Pitblado (2010).The various satellite LNG tanks are normally surrounded by huge containment that act as limits to the spread of an unprecedented LNG spill as well as the size of the potential vapor cloud as pointed out by Gaul and Young (2003). The risks in this mode of LNG transport are of highway collisions, spills on loading, truck rollover as well as storage tank leaks. The scale is usually smaller but the event frequency is noted to be higher as compared for the ones for LNG import terminals as well as the regasification systems.

Receiving LNG and its regasification

This is the fourth stage in the LNG handling process. This chain involves the marine terminals where the LNG is stored before it is reconverted back to gas thus, regasification. There are currently about 60 LNG terminals used in the import handling of the LNG which operate worldwide. The largest importers of LNG are Korea, Japan, Taiwan, India in Asia while in the Americas, the largest importers are USA, Mexico, Brazil, Argentina, and Chile and in Europe, the list includes; Belgium, UK, Italy, Spain and Portugal.